symmetric property

If a property P is symmetric, and the property relates individual a to individual b then individual b is also related to individual a via property P. For example, if the individual Matthew is related to the individual Gemma via the hasSibling property, then we can infer that Gemma must also be related to Matthew via the hasSibling property. In other words, if Matthew has a sibling that is Gemma, then Gemma must have a sibling that is Matthew. Put another way, the property is its own inverse property.